In co-pending U.S. patent application Ser. No. 08/992,443, filed by the applicant on Dec. 17, 1997, there is disclosed a lock apparatus including a lock shell, a cylindrical lock core unit received in the lock shell and having an axial key hole and being provided with a latch actuator, and a coded key. The coded key is extendible into the key hole of the lock core unit, and is operable so as to permit rotation of the lock core unit relative to the lock shell for moving the latch actuator from a locking position to an unlocking position.
The key has a head portion and a shank portion that extends from the head portion. The shank portion has a cross-section in the form of a circular section with first and second planar surfaces that extend along length of the shank portion, and a curved sector that interconnects the first and second planar surfaces and that has an arc length greater than 180 degrees. The shank portion is formed with a plurality of key bit projections and key bit grooves on one of the first and second planar surfaces. The key bit projections and the key bit grooves have inclined actuating surfaces that form different angles with the first and second planar surfaces to set code of the key.
The lock shell is formed with an axially extending locking groove. The lock core unit includes a cylindrical inner shell disposed in the lock shell, and is formed with an axially extending locking slot that is registered with the locking groove when the lock core unit is in the locking position, and a stack of annular locking plates. Each of the locking plates has an inner periphery that confines a central hole. The central holes of the locking plates define cooperatively the key hole of the lock core unit. Each of the locking plates further has an outer periphery that is formed with an engaging notch. The engaging notches of the locking plates are misaligned with one another in accordance with the code of the key when the lock core unit is in the locking position, and are aligned with one another when the lock core unit is in the unlocking position. The inner periphery of each of the locking plates is formed with a radial inward key engaging protrusion. The key engaging protrusion has a first radial edge to abut against the actuating surface of a corresponding one of the key bit projection and the key bit grooves on the key when the key is received in the key hole and is rotated to unlock the lock core unit, thereby permitting rotation of the locking plates by different angles corresponding to the angles of the actuating surfaces of the key bit projections and the key bit grooves on the key in order to align the engaging notches on the locking plates.
The key engaging protrusion further has a second radial edge opposite to the first radial edge to abut against the other one of the first and second planar surfaces of the shank portion of the key when the key is received in the key hole and is rotated to lock the lock core unit, thereby permitting rotation of the locking plates in order to misalign the engaging notches on the locking plates according to the code of the key.
A locking rod is received in the locking slot of the inner shell. Misalignment of the engaging notches on the locking plate enables the outer peripheries of the locking plates to force the locking rod to extend into the locking groove of the lock shell in order to prevent rotation of the inner shell relative to the lock shell when the lock core unit is in the locking position. Alignment of the engaging notches on the locking plates enables the locking rod to disengage the locking groove and to engage the engaging notches in order to permit rotation of the inner shell relative to the lock shell when the lock core unit is in the unlocking position.
The lock core unit further includes an annular drive plate disposed in the inner shell between the latch actuator and the locking plates. The drive plate has a key engaging inner periphery and an outer periphery formed with a radial cam projection. The inner periphery of the drive plate engages the shank portion of the key when the key is received in the key hole for co-rotation therewith. The latch actuator has a cam actuatable section which is driven by the radial cam projection of the drive plate such that rotation of the drive plate can result in corresponding rotation of the latch actuator between the locking and unlocking positions.
Some of the disadvantages of the aforesaid lock apparatus are as follows:
(a) The radial cam projection of the drive plate is shaped as a circular sector less than half of a circle in arc length and defines two radial cam edges, thereby defining in cooperation with the inner shell an arc groove between the radial cam edges such that the drive plate may wobble in a radial direction relative to the inner shell to result in misalignment of the key engaging inner periphery of the drive plate with respect to the radial inward key engaging protrusions of the locking plates, thereby hindering smooth insertion of the correct key into the lock core unit for actuating the latch actuator from the locking position to the unlocking position.
(b) The front end of the lock shell is not provided any anti-theft means in order to prevent a picking tool, such as a drill, from reaching an interior of the lock shell and hence the lock core unit.